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Open Theses

You may also contact one of our doctoral candidates directly, if you are interested in a Bachelor or Master thesis, a student job, an "Ingenieurspraxis" or a "Forschungspraxis". It often happens, that topics are being prepared which are not adverdised yet. It may also be possible to find a topic matching your specific interests.Please include a curriculum vitae together with a list of attended courses when applying for a thesis.If your "Ingenieurspraxis" is selected to be supervised by one of our professors, please hand in the documents to Doris Dorn (Room N2401).

Master/Diploma Theses

Multi-user communication systems (such as wireless systems) are different than point to point channels in two key aspects; namely, the broadcast nature of transmissions (e.g., wireless transmissions can be picked up by any receiver in the vicinity of the transmitter) and the superposition (e.g., a wireless receiver picks up a linear combination of transmissions from all transmitters in its vicinity). Recently a deterministic approach to multi-user information theory has proved promising by achieving progress in some of the long-standing open problems by finding approximate solutions. The idea behind a deterministic approach, on a high level, is to focus on the interaction of signals rather than the background noise, through a simpler appropriate model; find exact solutions for the simpler model; and then translate the intuitions and techniques to new techniques and/or approximate solutions on noisy models.
The goal of thesis is to undertake a deterministic approach to Gaussian MIMO broadcast channels.
Prerequisite: Linear Algebra, Information Theory

This project intends to investigate the role of feedback in broadcast channels. More information available upon request.
Pre-requisite (at least one of the following):
Basic knowledge of Network Coding (see [2])
Basic knowledge of Algorithms
Basic knowledge of Information Theory

Project description
Research on optical communication systems is nowadays focusing on methods and technologies which would allow higher capacity and increased transmission distance. The capacity of optical communication systems can be increased by a combination of spectrally efficient modulation formats and advanced receiver design. Currently, commercially available optical communication systems employ modulation formats that carry 2 bits/symbol/polarization, such as quadrature phase shift keying. In the near future, it is expected that in order to satisfy capacity demands, it will be required to increase the spectral efficiency to 4 or even 6 bits/symbol/polarization. This would require moving to 16 or 64 quadrature amplitude modulation (QAM).
Moreover, there is a strong focus on designing optical systems with reduced footprint and this requires large scale integration of optical components including semiconductors lasers. The semiconductor lasers exhibit a non-Lorentzian lineshape due to carrier induced frequency noise. This noise presents itself mainly as a resonance peak on the frequency noise power spectral density (PSD), which has been shown to play an important role on the system performance [4]. If phase noise tracking algorithms are not properly designed a large penalty in system performance may be obtained for higher order modulation formats (> 16 QAM) [4-5]. For non-Lorentizan lineshape more sophisticated tracking algorithms are therefore needed as the physics behind the laser phase noise process needs to be taken into account. As a proof-of-principle, it has been demonstrated theoretically and experimentally that Bayesian filtering methods are an effective tool in tracking phase noise that exhibits non-Lorentizan lineshape [5-6]. One of the challenges with Bayesian tracking methods is that they require knowledge of the parameters of the state-space describing the system. This is especially challenging to infer from the measured data due to the high dimensionality of the state-space as well as that the measured systems have typically a large number of unknown variables [7].

Objectives of the project
The main topic of this Master Project is implementation of Bayeisan inference techniques for parameter identification of state-space model for optical sources exhibiting non-Lorentzian lineshapes. The student will develop framework for parameter estimation based on expectation maximization which is an iterative approach for maximum likelihood parameter estimation. The inferred knowledge about the state-space will then be used to formulate digital signal processing algorithms for carrier phase noise compensation for coherent optical communication systems. If time allows, the student will test the framework on experimental data obtained for an optical transmission systems employing long haul transmission and higher order model formats.

Scope:I offer master thesis topics in the area of modulation, signaling and channel coding. The goal is to design transmission schemes for reliable communication close to the theoretical limits. We consider wireless, optical and wired communication channels and take power, bandwidth, and latency constraints into account.

Prerequisites: you should have attended one or more of the following courses: Information Theory, Channel Coding, Coded Modulation, Channel Codes for Iterative Decoding.

The thesis consists of finite-length code design for security primitives. You will be given a particular security primitive whose details will be provided and easy to understand. Then, independent of the secrecy part you will be given the channel parameters, desired block lengths and BERs so that we can design the "best" code (i.e., decoder) for that particular short length with low complexity.
Prerequisites: Channel Coding lecture is necessary, any other advanced channel coding lecture is a plus.
You can apply by email with your CV and transcript. You can also start to work on the topic as an internship before the thesis starts.

Ingenieurspraxis

The student will take care of following tasks
1. Modify the Matlab code for PCM lab experiment to make it compatible with the current audio interface.
2. Modernize the Graphical User Interface for the experiment.
3. Improve the description and the assignments for the experiment.

Forschungspraxis (12 ECTS)

Candy Crush Codes [1] are a stupid idea for non-linear block codes whose constraints are taken from the game rules of Candy Crush Saga. Although the codes themselves will not be "good" in a communication-theoretic sense, they are at least interesting in their combinatorial properties or for didactic reasons. Moreover, even though the first step will be to look at block codes, it should be possible to encode and decode also sequentially, essentially admitting infinite blocklengths.

This research internship should investigate the code's combinatorial properties (i.e., rate as function of field size and candy flavors), en- and decoding schemes, error probabilities for M-ary symmetric channels, and, if possible, improve code design such that the codes become useful (e.g., have a guaranteed Hamming distance). At the basis of all these investigations is of course a detailed literature survey of nonlinear codes with two-dimensional constraints.

Theses in Progress

Bachelor Theses

Random Linear Network Coding (RLNC) is a powerful approach to achieve the capacity in multicast networks.
Subspace codes are an efficient family of error correction codes in RLNC.
The idea behind these codes is to map information on a subspace and to transmit a basis for this subspace.
In this thesis, a model incorporating soft-information (reliability information) of the received packets (basis vectors) using a linear inner code is considered.
First the student should become familiar with linear block codes (e.g BCH, Reed--Solomon codes), concatenated coding schemes and the basics of Generalized Minimum Distance (GMD) decoding. In the next step, suitable inner codes to acquire the reliability information of the received packets should be chosen and implemented in MATLAB.
The performance of the coding schemes should be evaluated and compared by performing simulations in MATLAB.

Balance problems are beautiful mathematical puzzles, an instance of which goes like that: "There are nine balls, one of which is heavier. You have a balance scale. How many weighings are necessary to determine the heavy ball?" To this particular instance, the answer is two [1]. That two weighings are not only sufficient, but also necessary (i.e., two weighings are optimal), can be shown using information theory: The uncertainty about the heavy ball is equal to the information that is obtained with two weighings. There are several variations on this problem: Arbitrary numbers of balls can be considered, or it may be unknown whether the oddball is heavier or lighter than the rest. We believe that information theory can tell us something about these variations, too. In this
thesis, these variations will be analyzed using standard tools from information theory: conditional entropy and the chain rule. Finally, the connection to non-coherent demodulation of pulse-position-modulated signals will be investigated.

Spatially coupled (SC-) LDPC codes are known to reach capacity. Yet, it is unknown what the advantages in the finite-length regime are.
The task of the student is to compare coupled LDPC codes with their underlying counterpart for finite code lengths using finite-length scaling laws and to verify the results by simulations.

Master/Diploma Theses

The robustness of the channel estimation is a key for coherent spatial division multiplexing OFDM transmission system. Time-multiplex(TM) preamble structure has been widely adopted in the polarisation division multiplexing OFDM transmission and in the scenario of spatial division multiplexing OFDM transmission supporting 3 spatial modes. When scaling to higher number of spatial modes, the TM based channel estimation introduces huge overhead and is sensitive to laser phase noise. Therefore, subcarrier-orthogonal(SO) preamble structure is a potential candidate for channel estimation.
In this work, the TM and SO preamble-based channel estimation will be investigated under the influence of laser phase noise, mode-dependent loss and strong/weak coupling regime of the few mode fiber.

This master thesis is in cooperation with the radio communications department at Rohde&Schwarz.
Airborne radio communication is based on Amplitude Modulation (AM). To use them with existing low-directivity antennas in airplanes, the effects of multipath propagation have to be considered. The student will investigate the channel effects on airborne communications (Ground-Air, Air-Air) and compare possible receiver designs. For this aim, realistic multipath-propagation scenarios will be defined for airborne communications. The models and the suggested designs will be tested with Matlab/Simulink. The student will evaluate the results and compare multiple techniques to improve communication quality.

The purpose of this thesis is to investigate state space aggregation methods using information-theoretic cost function. The main cost functions investigated shall be the I(Y_1;Y_2) and H(Y_2|Y_1) - H(Y_2|X_1). The former, which should be maximized, is related to information-theoretic clustering and to near complete decomposability of Markov chains. The latter, which should be minimized, is related to lumpability, the phenomenon of a function of a Markov chain being Markov. Both cost functions should be optimized over all possible partitions of the state space, which is a combinatorial problem.

In order to reduce the computational complexity of the search, sub-optimal aggregation methods shall be adopted from the literature: Agglomerative, sequential, or splitting methods shall be investigated. Furthermore, it is interesting to see if a relaxation of the cost functions admits the application of established algorithms, like the information bottleneck method.

The aggregation methods shall be evaluated at the hand of a few examples, e.g., quasi-lumpable and nearly completely decomposable Markov chains, examples from natural language processing or synthetic biology, and the Ehrenfest diffusion model.

The performance of non-binary LDPC (NB-LDPC) codes on the binary erasure channel (BEC) is analyzed.
Existing analysis tools of their binary counterparts are extended for NB-LDPC codes.
Therefore, the binary extension of the NB-LDPC codes is constructed and its behaviour is investigated analytically.

Tasks & Responsibilities:
- Architect, design, code, debug, test and document new/existing designs with a major focus on the embedded hardware elements of the design
- Work to minimize the need for third party development resources bringing into balance in-house vs. outsourced services
- Collaborate with HW designers on the selection of components for new designs where applicable
- Develop test procedures and support design of test and design qualification systems-
- Provide documentation of all designs

Positioning is one of the most important fields of application for wireless radio transmissions. In critical environments, such as urban canyon or indoors, the position accuracy using wireless signals is drastically reduced. In these environments, multipath effects, low received signal power and non-line-of-sight propagation reduce the position accuracy. With Channel-SLAM, we proposed a paradigm shift in how to process the received signal in order to provide accurate position estimation for mobile receivers: rather than mitigating multipath, we propose to exploit multipath. Channel-SLAM treats multipath components as signals emitted from virtual transmitters which are time synchronized to the physical transmitter and static in their position. Hence, multipath propagation increases the number of transmitter by virtual transmitters resulting in more accurate position estimation or enabling positioning in situations where the number of physical transmitters is insufficient. Channel-SLAM estimates the receiver position and the positions of the virtual transmitters simultaneously and does not require any prior information such as room-layout or a database for fingerprinting.
This Master thesis builds on and extends the previous work on Channel-SLAM. In order to exploit multipath components for multiple receivers, this Master thesis shall derive a mapping algorithm for virtual transmitters. The positions of virtual transmitters do not change over time, however, the virtual transmitters are only visible in a certain area. Hence, each virtual transmitter can be described by a static position and a visibility region. Thus, this master thesis shall derive a representation of the visibility region of virtual transmitters and shall extend the current Channel-SLAM approach. Additionally, the results should be verified by simulations and measurements. The results might give valuable geometric information on the locations of reflector and scatterers, which might enable to obtain geometric information of all kinds of environments by using wireless signals.

Software Defined Radio is a relatively new concept in thinking and designing communications systems. What defines it is that almost all parts of a transciever (transmitter/receiver) are implemented as software modules on a general purpose computer, rather than on dedicated hardware. The radio frequency part of the receiver is thus also reconfigurable through software and will represent just an interface.

Simulink is a graphical programming tool from Mathworks and is especially good for fast prototyping and simulating of complex systems. It provides many custom made software modules and light and easy way to set up graphical user interfaces.

The purpose of this project is that following the principles of SDR radio and the facilities offered by Matlab/Simulink you could build a real-time receiver for digital modulated transmissions.
Links:

Forschungspraxis (12 ECTS)

The Nonlinear Schrödinger Equation (NLSE) is a nonlinear partial differential equation that describes the propagation of light in a nonlinear optical fiber. Since there is no closed-form solution to the NLSE, numerical methods are used to approximately solve it. The most popular among these methods is the split-step Fourier method (SSFM).
The student’s task in this Forschungspraxis/Ingenieurspraxis is to implement the SSFM in Matlab-Enabled C (mex) with CUDA support.

Staircase codes are a relatively new class of algebraic channel codes for high-speed optical communications. Their large coding gains and reasonable decoding complexity have made them a promising option for data rates of 100 Gbit/s and more.
The student's task of this Forschungspraxis is to understand the concept of staircase codes and implement them in Matlab or C.